| From | "Paul E. McKenney" <> | Subject | [PATCH RFC tip/core/rcu 05/11] rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT. | Date | Tue, 22 Feb 2011 17:39:34 -0800 |
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The build will break if you change the Kconfig to allow DEBUG_OBJECTS_RCU_HEAD and !PREEMPT, so document the reasoning near where the breakage would occur.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> --- kernel/rcupdate.c | 5 +++++ 1 files changed, 5 insertions(+), 0 deletions(-)
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c index afd21d1..f3240e9 100644 --- a/kernel/rcupdate.c +++ b/kernel/rcupdate.c @@ -214,6 +214,11 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state) * Ensure that queued callbacks are all executed. * If we detect that we are nested in a RCU read-side critical * section, we should simply fail, otherwise we would deadlock. + * Note that the machinery to reliably determine whether + * or not we are in an RCU read-side critical section + * exists only in the preemptible RCU implementations + * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why + * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT. */ if (rcu_preempt_depth() != 0 || preempt_count() != 0 || irqs_disabled()) { -- 1.7.3.2
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